CA qualification is a professional qualifcation associated with British Commonwealth countries. Upon graduation of the CA program you will receive a Graduate Diploma in Chartered Accounting, whereas, the CPA is a series of exams for membership into the CPA Australian.
CA is the main professional accounting qualification within the Australian Big 4. In order to become an equity partner within a "chatered accounting firm" let's say Big 4, you have to complete the CA program. However, there are staff within Big 4 who complete the CPA program for their own career and personal reasons. For CPAs with 10 years experience in chartered accounting, they are eligible for membership into the ICAA.
There is no such thing as the CA is better or superior than the CPA. The ICAA and CPA Australia are 2 professional bodies with similar codes of conduct and ethical requirements. Both are recognised in the business world, however, the CPA is more industry-focused qualification. That is not to say that the CA isn't.
From an international perspective it does not matter if you get the CA or CPA. If you want to work in the US, you still require conversion exams. Even in the US, US CPAs within one state cannot practice in another. If one's intention is to work in Australia or other Commonwealth countries, then a CA is more desirable and appropriate.
It is without a doubt that the CA Program is much harder than the CPA Program. I currently work in Big 4 and the majority of the people complete the CA Program. CA Program is much more stringent and rigorous because they have 5 set subjects for candidates to complete, whereas, CPA you can choose from a variety of subjects. For the CA Program, there is only 3 marks you can get "Pass", "Merit" or "Fail". Majority of the CA candidates will be extremely happy for a "Pass". To get a Merit you have to get within the top 5% of the state, and for someone that is working full-time it is extremely difficult to find time to study enough to get within reach of top 5% of the state.
For those that intend to pursue a career in Big 4 accounting, I strongly suggest the CA program.
Just my 2 cents.